Filament support for vacuum tubes



March 6, 1928.

1,662,032 D. A. MULLANEY FILAMENT SUPPORT FOR VACUUM TUBES Filed Oct. 9. 1924 Inventor: Dudley A. TTluI lahey,

His Attorney.

Patented Mar. 6, 1928.

UNITED STATES DUDLEY A. HULLANEY, OF SCHENECTADY, NEW YORK, ASSIGNOR T GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK. I

FILAHENT SUPPORT FOR VACUUM TUBES.

Application filed October 9, 1924. Serial No. 742,683.

The filament or cathode of a space current device must be placed in close proximity to 1 its cooperating electrodes such as the anode and rid in order to be in electron responsive .relatlon to the same. It is obvious therefore that the small amount of clearance available necessitates the accurate position ZO-ing' of said elements in order to revent short circuiting of the filament with the other electrodes.

The filament consequently must be sup ported in a relatively rigid manner, and to.

etfect this result the loops of the filament are generally retained byflhooks which in turn may be attached to menibers supporting the grid or control electrode, and, sometimes, the anode.

When the grid and anode supporting structure is made of metal it is, of course necessary to insulate the filament retaining hooks therefrom. Various expedients have been proposed to effect this purpose. Thus, glass tubes and glass rods have been used and disposed intermediate the filament re taining hook and the anode support, the re-.

taining hook being either sealed into the glass tube or rod or else'held thereon by means of suitable clamps. When such hooks are sealed into the glass it necessitates the use of a wire which will form a satisfactory seal with the glass, so that if the coeflicient of expansion of the wire varies appreciably from that of the glass, or if the wire is not wet by the glass there may be a tendency for the glass to crack. When clamped or tied into place, on the other hand, it is impossible to effect a lasting rigid connection, since the stresses engendered by theheat will inevitably loosen the wire.

One of the objects of my invention is to provide a simple type of filament support PATENT OFFICE.

which will withstand prolonged exposure to heat without disintegration.

Another object of my invention is to provide a support which will permit of the use of any desired type of metallic filament retaining device.

A further object of my invention is so to simplify the construction of the support that it maybe assembled readily and rapidly without the aid of skilled glass blowers.

\Vith these objects in view my invention will best be understood by reference to the following description taken -in connection with the accompanying drawing, while the scope of the invention will be pointed out more particularly in the appended claims.

In the drawing Figure 1 illustrates a portion of a space current device of one type illustrating the respective positions of the cathode, anode and grid and showing the disposition therein of the filament retaining device or support of the invention.

Figures 2, 3 and 4 show enlarged sectional views of modifications of the filament support.' In the drawing the space current device of Fig. 1 is used as an illustration of the method in which the filament support may be used. It is to be understood, however, that the figure is merely illustrative so that the disposition of the elements of the device may vary, and, furthermore that the filament su port may be used in other devices than vacuum tubes, for example electric incandescent lamps, all without departing from the scope of the invention. In Fig. 1 the filament is represented by 2 and the supporting structure from which the filament support'is suspended or attached is indicated by 15.

Referring in detail to the drawing the filament support of the invention as shown in its preferred embodiment in Figs. 2, 3, and 4 consists of a rod or body member of fused quartz 10 either transparent or opa ue, into each end of which wires 11, 12 pre erably of mol bdenum are firmly embedded:

. In embed ing the metal members 11 and 12 in the quartz insulators 10 I prefer to use a modification of the method disclosed in the U. S. Patent No. 832,302 of 1906 to C. A. Ernst. According to this method a plurality of short metal members.are placed at spaced intervals inside of a closed glass are not held by the quartz with the same degree of intimacy as in the case of glass inasmuch as quartz will not wet the surface of thewire. lVith some metals the formation of a thin layer of oxide which is insoluble in the quartz precludes the formation of a wet seal while with other metals the coefficient of expansion is such as to prevent the formation of a tight seal. Wires and other metallic members when embedded in.

fused quartz are therefore relatively loosely held since the joint is a purely mechanical one. I have, however, discovered that by nicking or notching the wire in a suitable manner as shown for example at 4 in Figs. 2, 3, and 4. it will be held firmly by the quartz and that this constitutes a satisfactory heat resisting mechanical seal. This method of insuring the retention of the wire by the quartz is of course merely illustra-' tive and any equivalent treatment of the wire such as fraying, bending, or flattening may /be used to effect the same purpose. Furthermore, any desired type of metallic member ma be embedded in the quartz providing simi ar means are-used to insure the retention of the member by the quartz.

Although the filamentsupport shown in Fig. 2 represents the preferred construction of my device the same maybe modified as shown in Fig. 4 without departing from the scope of the invention by interposing the filament tensioning springs 13 between the filament retaining hook 14 and the embed tweenthe hooks 12 and the filament as indicated in Fig. 1. If the construction of the tube requires it the support may be constructed as inFig. 3, omitting the metallic member 11 of Fig. 1 by means of which the device is ordinarily secured within a vacuum tube,.so that the'quartz body may nceaoaa be attached directly to any convenient struc tural element of the tube, e. g. the supporting member indicated by 15 in Fig. 1.

The filament support formed as hereinbefore described may be mounted in a space current or analogous e. g. an electric incandescent lamp in any suitable manner. Thus, one of the metal rods 11 may be attached directly to the grid or anode supports by spot welding or other means.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. An insulating support for an incandescent filament comprising a body member of'fused quartz and a metallic filament retaining member whose one end is adapted to receive a filament and whose other end is embedded in said fused quartz body memher, said other end being notched so that said member may be retained in position in the quartz when subjected to tension and to the heat of the filament.

2. An insulating support for an incandescent filament comprising a body member- 0f I fused quartz, means embedded in one extremity of said body member and adapted to receive a filament and metallic means associated with the other extremity of said body member and adapted to' retain said insulating support in operative relation to a filament.

3. A support for incandescent filaments comprising an elongated quartz insulator, a

metallic member embedded in said insulator at one end thereof and adapted to engage a filament, a second, metallic member axially disposed with respect to said first mentioned .member and embedded in the opposite end of the insulator, said second member being adapted to serve as a suspension aneans for said insulator. 1 i y 4. A support for incandescent filaments comprising an elongated quartz insulator, metallic members spaced apart from one another and embedded in said insulator at opded member 12, instead of locating them be posite ends thereof, the embedded portions of said members being rovided with notches whereby they may e retained in position in the insulator when subjected to 

